There have been a plurality of attempts over the last several decades to incorporate electronic swing analyzing devices directly into golf clubs, particularly into "wood" clubs, bearing in mind that today's "wooden clubs" are constructed of metal and other materials such as compression molded graphite, besides natural wood.
Such swing analyzing devices include swing angle sensing devices that use orthogonally related accelerometers located within the club head to provide club head deceleration signals occurring during impact to analyzing circuitry located externally of the club head, and a ball distance computer driven by a single accelerometer mounted within the club head providing club head deceleration signals to an analyzing circuitry mounted within the club head grip.
While there appears to be a demand for such self-contained club swing analyzing devices, none has achieved any degree of commercial success thus far for a plurality of reasons. Firstly, there has been a general misunderstanding in the prior art with respect to the physics involved in club-ball collision, and there has also been a failure to provide accurate conditioning signal production and proper signal modification to achieve a proportional representation of the sensed condition. For example, in a known distance computer, an accelerometer is employed to sense club head deceleration during and after ball impact. While club head deceleration is one parameter that determines ball exit velocity from the club face, it cannot by itself provide an accurate determination of ball exit velocity without knowing the time of impact between the ball and the club or initial club head velocity. The correct collision theory formula for determining ball exit velocity V.sub.b2 is m.sub.1 V.sub.b1 +.intg.Fdt=m.sub.2 V.sub.b2, where the V.sub.b1 =initial ball velocity, m.sub.1 =initial mass of ball, F=impact force between the ball and the club, and t=the time of impact between the ball and the club, m.sub.2 =final ball mass, and V.sub.b2 =the exit velocity of ball from the club. A similar equation may be derived with respect to the club head as opposed to the ball during collision.
Since initial ball velocity is zero and mass m is constant, it can readily be seen that final ball velocity V.sub.b2 is proportional to the integral .intg.Fdt or more simply expressed, exit ball velocity is proportional to the average impact force between the ball and the club head multiplied by the time duration of impact. Thus one problem in prior art devices for measuring ball distance is that they do not take into account the duration of impact between the ball and the club.
This time duration of impact can be expressed in laymen's terms as the follow-through of the club impacting on the ball, and the longer the time period of impact the greater the exiting ball velocity and the greater the distance the ball travels.
Another deficiency in built-in swing analyzing devices and particularly ball distance computers is that known sensing or transducing devices cannot be readily built into the club head either because they are not sufficiently durable or because they alter the weight, swing-weight or torquing characteristics of the club. Even a small additional weight added to the club head alters swing-weight significantly, for example 1.0+ grams added to the club head increases the swing-weight of the club one full swing-weight, e.g. from D-1 to D-2, in addition to increasing the overall weight of the club head. While this weight addition can be compensated in terms of swing weight by adding weight to the butt end of the shaft, such a compensating maneuver is not desirable because it further increases the overall weight of the club. Thus, these prior built-in sensing and computing devices have not been acceptable because they either varied the club's swing weight or the overall weight of the club, or both.
Built-in swing sensing and computing devices have also not demonstrated an acceptable level of durability to withstand the high force impact, frequently over 50 lbs., generated in the few milliseconds or less of impact time.
Furthermore, in all of the prior literature on built-in swing analyzing devices there is a notable lack of technology with respect to specific transducer constructions and the exact method of attaching the transducer to the club head.
Another problem in these prior systems is that they do not take into account the non-linear relation between ball-club impact and ball travel distance.
A ball distance computing device manufactured by Mitsubishi Corp. has achieved some degree of commercial success even though the sensing device, computer circuitry and visual display are external to the club head. This system utilizes a Hall effect transducer in a floor mat driven by magnetic tape attached to the club head, and while this system has been found satisfactory for many purposes, it produces inaccuracies in the ball distance computing function because of the failure to measure ball impact time, because of misapplication of the magnetic tape to the club head and failure to account for club head mass, and because exact club head loft angle is not considered, all of which control ball travel distance.
An example of a built-in ball distance computer is shown and described in the Farmer U.S. Pat. No. 4,088,324 and it utilizes an accelerometer in the club head in an attempt to compute ball distance. Accelerometers built into the club head are also shown in the Evans U.S. Pat. Nos. 3,788,647; 3,806,131 and 3,270,564 as well as the Hammond U.S. Pat. No. 3,945,646, for generating information relating to ball striking direction as well as club velocity and acceleration.
It is a primary object of the present invention to ameliorate the problems noted above in club built-in swing analyzing devices and particularly to club self-contained distance computers.